wsutil/crc16.c

   1 /* crc16.c
   2  * CRC-16 routine
   3  *
   4  * 2004 Richard van der Hoff <richardv@mxtelecom.com>
   5  *
   6  * $Id$
   7  *
   8  * Wireshark - Network traffic analyzer
   9  * By Gerald Combs <gerald@wireshark.org>
  10  * Copyright 1998 Gerald Combs
  11  *
  12  * This program is free software; you can redistribute it and/or
  13  * modify it under the terms of the GNU General Public License
  14  * as published by the Free Software Foundation; either version 2
  15  * of the License, or (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software
  24  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  25  *
  26  * References:
  27  *  "A Painless Guide to CRC Error Detection Algorithms", Ross Williams
  28  *      http://www.repairfaq.org/filipg/LINK/F_crc_v3.html
  29  *
  30  *  ITU-T Recommendation V.42 (2002), "Error-Correcting Procedures for
  31  *      DCEs using asynchronous-to-synchronous conversion", Para. 8.1.1.6.1
  32  */
  33
  34 #include "config.h"
  35
  36 #include <glib.h>
  37 #include <wsutil/crc16.h>
  38 #include <wsutil/crc16-plain.h>
  39
  40
  41 /*****************************************************************/
  42
  43 /*
  44  * Table for the CCITT/ITU/CRC-16 16-bit CRC
  45  *
  46  * Polynomial is
  47  *
  48  *     x^16 + x^12 + x^5 + 1
  49  */
  50
  51 /*                                                               */
  52 /* CRC LOOKUP TABLE                                              */
  53 /* ================                                              */
  54 /* The following CRC lookup table was generated automagically    */
  55 /* by the Rocksoft^tm Model CRC Algorithm Table Generation       */
  56 /* Program V1.0 using the following model parameters:            */
  57 /*                                                               */
  58 /*    Width   : 2 bytes.                                         */
  59 /*    Poly    : 0x1021                                           */
  60 /*    Reverse : TRUE.                                           */
  61 /*                                                               */
  62 /* For more information on the Rocksoft^tm Model CRC Algorithm,  */
  63 /* see the document titled "A Painless Guide to CRC Error        */
  64 /* Detection Algorithms" by Ross Williams.  See                  */
  65 /*                                                               */
  66 /*    http://www.ross.net/crc/crcpaper.html                      */
  67 /*                                                               */
  68 /* which links to a text version and an HTML-but-not-all-on-one- */
  69 /* page version, or various HTML-all-on-one-page versions such   */
  70 /* as the one at                                                 */
  71 /*                                                               */
  72 /*    http://www.geocities.com/SiliconValley/Pines/8659/crc.htm  */
  73 /*                                                               */
  74 /* (search for the title to find others).                        */
  75 /*                                                               */
  76 /*****************************************************************/
  77
  78 static const guint crc16_ccitt_table_reverse[256] =
  79 {
  80  0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
  81  0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
  82  0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
  83  0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
  84  0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
  85  0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
  86  0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
  87  0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
  88  0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
  89  0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
  90  0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
  91  0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
  92  0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9,
  93  0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1,
  94  0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738,
  95  0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70,
  96  0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7,
  97  0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF,
  98  0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036,
  99  0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E,
 100  0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5,
 101  0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD,
 102  0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134,
 103  0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C,
 104  0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3,
 105  0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB,
 106  0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232,
 107  0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A,
 108  0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1,
 109  0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9,
 110  0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330,
 111  0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78
 112 };
 113
 114 /* Same as above, only without reverse (Reverse=FALSE) */
 115 static const guint crc16_ccitt_table[256] =
 116 {
 117  0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
 118  0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
 119  0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
 120  0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
 121  0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
 122  0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
 123  0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
 124  0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
 125  0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
 126  0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
 127  0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
 128  0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
 129  0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
 130  0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
 131  0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
 132  0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
 133  0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
 134  0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
 135  0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
 136  0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
 137  0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
 138  0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
 139  0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
 140  0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
 141  0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
 142  0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
 143  0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
 144  0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
 145  0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
 146  0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
 147  0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
 148  0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
 149 };
 150
 151 /* This table was compiled using the polynom 0x5935 */
 152 static const guint crc16_precompiled_5935[256] =
 153 {
 154         0x0000, 0x5935, 0xB26A, 0xEB5F, 0x3DE1, 0x64D4, 0x8F8B, 0xD6BE,
 155         0x7BC2, 0x22F7, 0xC9A8, 0x909D, 0x4623, 0x1F16, 0xF449, 0xAD7C,
 156         0xF784, 0xAEB1, 0x45EE, 0x1CDB, 0xCA65, 0x9350, 0x780F, 0x213A,
 157         0x8C46, 0xD573, 0x3E2C, 0x6719, 0xB1A7, 0xE892, 0x03CD, 0x5AF8,
 158         0xB63D, 0xEF08, 0x0457, 0x5D62, 0x8BDC, 0xD2E9, 0x39B6, 0x6083,
 159         0xCDFF, 0x94CA, 0x7F95, 0x26A0, 0xF01E, 0xA92B, 0x4274, 0x1B41,
 160         0x41B9, 0x188C, 0xF3D3, 0xAAE6, 0x7C58, 0x256D, 0xCE32, 0x9707,
 161         0x3A7B, 0x634E, 0x8811, 0xD124, 0x079A, 0x5EAF, 0xB5F0, 0xECC5,
 162         0x354F, 0x6C7A, 0x8725, 0xDE10, 0x08AE, 0x519B, 0xBAC4, 0xE3F1,
 163         0x4E8D, 0x17B8, 0xFCE7, 0xA5D2, 0x736C, 0x2A59, 0xC106, 0x9833,
 164         0xC2CB, 0x9BFE, 0x70A1, 0x2994, 0xFF2A, 0xA61F, 0x4D40, 0x1475,
 165         0xB909, 0xE03C, 0x0B63, 0x5256, 0x84E8, 0xDDDD, 0x3682, 0x6FB7,
 166         0x8372, 0xDA47, 0x3118, 0x682D, 0xBE93, 0xE7A6, 0x0CF9, 0x55CC,
 167         0xF8B0, 0xA185, 0x4ADA, 0x13EF, 0xC551, 0x9C64, 0x773B, 0x2E0E,
 168         0x74F6, 0x2DC3, 0xC69C, 0x9FA9, 0x4917, 0x1022, 0xFB7D, 0xA248,
 169         0x0F34, 0x5601, 0xBD5E, 0xE46B, 0x32D5, 0x6BE0, 0x80BF, 0xD98A,
 170         0x6A9E, 0x33AB, 0xD8F4, 0x81C1, 0x577F, 0x0E4A, 0xE515, 0xBC20,
 171         0x115C, 0x4869, 0xA336, 0xFA03, 0x2CBD, 0x7588, 0x9ED7, 0xC7E2,
 172         0x9D1A, 0xC42F, 0x2F70, 0x7645, 0xA0FB, 0xF9CE, 0x1291, 0x4BA4,
 173         0xE6D8, 0xBFED, 0x54B2, 0x0D87, 0xDB39, 0x820C, 0x6953, 0x3066,
 174         0xDCA3, 0x8596, 0x6EC9, 0x37FC, 0xE142, 0xB877, 0x5328, 0x0A1D,
 175         0xA761, 0xFE54, 0x150B, 0x4C3E, 0x9A80, 0xC3B5, 0x28EA, 0x71DF,
 176         0x2B27, 0x7212, 0x994D, 0xC078, 0x16C6, 0x4FF3, 0xA4AC, 0xFD99,
 177         0x50E5, 0x09D0, 0xE28F, 0xBBBA, 0x6D04, 0x3431, 0xDF6E, 0x865B,
 178         0x5FD1, 0x06E4, 0xEDBB, 0xB48E, 0x6230, 0x3B05, 0xD05A, 0x896F,
 179         0x2413, 0x7D26, 0x9679, 0xCF4C, 0x19F2, 0x40C7, 0xAB98, 0xF2AD,
 180         0xA855, 0xF160, 0x1A3F, 0x430A, 0x95B4, 0xCC81, 0x27DE, 0x7EEB,
 181         0xD397, 0x8AA2, 0x61FD, 0x38C8, 0xEE76, 0xB743, 0x5C1C, 0x0529,
 182         0xE9EC, 0xB0D9, 0x5B86, 0x02B3, 0xD40D, 0x8D38, 0x6667, 0x3F52,
 183         0x922E, 0xCB1B, 0x2044, 0x7971, 0xAFCF, 0xF6FA, 0x1DA5, 0x4490,
 184         0x1E68, 0x475D, 0xAC02, 0xF537, 0x2389, 0x7ABC, 0x91E3, 0xC8D6,
 185         0x65AA, 0x3C9F, 0xD7C0, 0x8EF5, 0x584B, 0x017E, 0xEA21, 0xB314
 186 };
 187
 188 /* This table was compiled using the polynom 0x755B */
 189 static const guint crc16_precompiled_755B[] =
 190 {
 191     0x0000, 0x755b, 0xeab6, 0x9fed, 0xa037, 0xd56c, 0x4a81, 0x3fda,     /* 0x00 */
 192     0x3535, 0x406e, 0xdf83, 0xaad8, 0x9502, 0xe059, 0x7fb4, 0x0aef,     /* 0x08 */
 193     0x6a6a, 0x1f31, 0x80dc, 0xf587, 0xca5d, 0xbf06, 0x20eb, 0x55b0,     /* 0x10 */
 194     0x5f5f, 0x2a04, 0xb5e9, 0xc0b2, 0xff68, 0x8a33, 0x15de, 0x6085,     /* 0x18 */
 195     0xd4d4, 0xa18f, 0x3e62, 0x4b39, 0x74e3, 0x01b8, 0x9e55, 0xeb0e,     /* 0x20 */
 196     0xe1e1, 0x94ba, 0x0b57, 0x7e0c, 0x41d6, 0x348d, 0xab60, 0xde3b,     /* 0x28 */
 197     0xbebe, 0xcbe5, 0x5408, 0x2153, 0x1e89, 0x6bd2, 0xf43f, 0x8164,     /* 0x30 */
 198     0x8b8b, 0xfed0, 0x613d, 0x1466, 0x2bbc, 0x5ee7, 0xc10a, 0xb451,     /* 0x38 */
 199     0xdcf3, 0xa9a8, 0x3645, 0x431e, 0x7cc4, 0x099f, 0x9672, 0xe329,     /* 0x40 */
 200     0xe9c6, 0x9c9d, 0x0370, 0x762b, 0x49f1, 0x3caa, 0xa347, 0xd61c,     /* 0x48 */
 201     0xb699, 0xc3c2, 0x5c2f, 0x2974, 0x16ae, 0x63f5, 0xfc18, 0x8943,     /* 0x50 */
 202     0x83ac, 0xf6f7, 0x691a, 0x1c41, 0x239b, 0x56c0, 0xc92d, 0xbc76,     /* 0x58 */
 203     0x0827, 0x7d7c, 0xe291, 0x97ca, 0xa810, 0xdd4b, 0x42a6, 0x37fd,     /* 0x60 */
 204     0x3d12, 0x4849, 0xd7a4, 0xa2ff, 0x9d25, 0xe87e, 0x7793, 0x02c8,     /* 0x68 */
 205     0x624d, 0x1716, 0x88fb, 0xfda0, 0xc27a, 0xb721, 0x28cc, 0x5d97,     /* 0x70 */
 206     0x5778, 0x2223, 0xbdce, 0xc895, 0xf74f, 0x8214, 0x1df9, 0x68a2,     /* 0x78 */
 207     0xccbd, 0xb9e6, 0x260b, 0x5350, 0x6c8a, 0x19d1, 0x863c, 0xf367,     /* 0x80 */
 208     0xf988, 0x8cd3, 0x133e, 0x6665, 0x59bf, 0x2ce4, 0xb309, 0xc652,     /* 0x88 */
 209     0xa6d7, 0xd38c, 0x4c61, 0x393a, 0x06e0, 0x73bb, 0xec56, 0x990d,     /* 0x90 */
 210     0x93e2, 0xe6b9, 0x7954, 0x0c0f, 0x33d5, 0x468e, 0xd963, 0xac38,     /* 0x98 */
 211     0x1869, 0x6d32, 0xf2df, 0x8784, 0xb85e, 0xcd05, 0x52e8, 0x27b3,     /* 0xA0 */
 212     0x2d5c, 0x5807, 0xc7ea, 0xb2b1, 0x8d6b, 0xf830, 0x67dd, 0x1286,     /* 0xA8 */
 213     0x7203, 0x0758, 0x98b5, 0xedee, 0xd234, 0xa76f, 0x3882, 0x4dd9,     /* 0xB0 */
 214     0x4736, 0x326d, 0xad80, 0xd8db, 0xe701, 0x925a, 0x0db7, 0x78ec,     /* 0xB8 */
 215     0x104e, 0x6515, 0xfaf8, 0x8fa3, 0xb079, 0xc522, 0x5acf, 0x2f94,     /* 0xC0 */
 216     0x257b, 0x5020, 0xcfcd, 0xba96, 0x854c, 0xf017, 0x6ffa, 0x1aa1,     /* 0xC8 */
 217     0x7a24, 0x0f7f, 0x9092, 0xe5c9, 0xda13, 0xaf48, 0x30a5, 0x45fe,     /* 0xD0 */
 218     0x4f11, 0x3a4a, 0xa5a7, 0xd0fc, 0xef26, 0x9a7d, 0x0590, 0x70cb,     /* 0xD8 */
 219     0xc49a, 0xb1c1, 0x2e2c, 0x5b77, 0x64ad, 0x11f6, 0x8e1b, 0xfb40,     /* 0xE0 */
 220     0xf1af, 0x84f4, 0x1b19, 0x6e42, 0x5198, 0x24c3, 0xbb2e, 0xce75,     /* 0xE8 */
 221     0xaef0, 0xdbab, 0x4446, 0x311d, 0x0ec7, 0x7b9c, 0xe471, 0x912a,     /* 0xF0 */
 222     0x9bc5, 0xee9e, 0x7173, 0x0428, 0x3bf2, 0x4ea9, 0xd144, 0xa41f      /* 0xF8 */
 223 };
 224
 225 /* This table was compiled using the polynom: 0x9949 */
 226 static const guint crc16_precompiled_9949_reverse[] =
 227 {
 228  0x0000, 0x0ED2, 0x1DA4, 0x1376, 0x3B48, 0x359A, 0x26EC, 0x283E,
 229  0x7690, 0x7842, 0x6B34, 0x65E6, 0x4DD8, 0x430A, 0x507C, 0x5EAE,
 230  0xED20, 0xE3F2, 0xF084, 0xFE56, 0xD668, 0xD8BA, 0xCBCC, 0xC51E,
 231  0x9BB0, 0x9562, 0x8614, 0x88C6, 0xA0F8, 0xAE2A, 0xBD5C, 0xB38E,
 232  0xFF73, 0xF1A1, 0xE2D7, 0xEC05, 0xC43B, 0xCAE9, 0xD99F, 0xD74D,
 233  0x89E3, 0x8731, 0x9447, 0x9A95, 0xB2AB, 0xBC79, 0xAF0F, 0xA1DD,
 234  0x1253, 0x1C81, 0x0FF7, 0x0125, 0x291B, 0x27C9, 0x34BF, 0x3A6D,
 235  0x64C3, 0x6A11, 0x7967, 0x77B5, 0x5F8B, 0x5159, 0x422F, 0x4CFD,
 236  0xDBD5, 0xD507, 0xC671, 0xC8A3, 0xE09D, 0xEE4F, 0xFD39, 0xF3EB,
 237  0xAD45, 0xA397, 0xB0E1, 0xBE33, 0x960D, 0x98DF, 0x8BA9, 0x857B,
 238  0x36F5, 0x3827, 0x2B51, 0x2583, 0x0DBD, 0x036F, 0x1019, 0x1ECB,
 239  0x4065, 0x4EB7, 0x5DC1, 0x5313, 0x7B2D, 0x75FF, 0x6689, 0x685B,
 240  0x24A6, 0x2A74, 0x3902, 0x37D0, 0x1FEE, 0x113C, 0x024A, 0x0C98,
 241  0x5236, 0x5CE4, 0x4F92, 0x4140, 0x697E, 0x67AC, 0x74DA, 0x7A08,
 242  0xC986, 0xC754, 0xD422, 0xDAF0, 0xF2CE, 0xFC1C, 0xEF6A, 0xE1B8,
 243  0xBF16, 0xB1C4, 0xA2B2, 0xAC60, 0x845E, 0x8A8C, 0x99FA, 0x9728,
 244  0x9299, 0x9C4B, 0x8F3D, 0x81EF, 0xA9D1, 0xA703, 0xB475, 0xBAA7,
 245  0xE409, 0xEADB, 0xF9AD, 0xF77F, 0xDF41, 0xD193, 0xC2E5, 0xCC37,
 246  0x7FB9, 0x716B, 0x621D, 0x6CCF, 0x44F1, 0x4A23, 0x5955, 0x5787,
 247  0x0929, 0x07FB, 0x148D, 0x1A5F, 0x3261, 0x3CB3, 0x2FC5, 0x2117,
 248  0x6DEA, 0x6338, 0x704E, 0x7E9C, 0x56A2, 0x5870, 0x4B06, 0x45D4,
 249  0x1B7A, 0x15A8, 0x06DE, 0x080C, 0x2032, 0x2EE0, 0x3D96, 0x3344,
 250  0x80CA, 0x8E18, 0x9D6E, 0x93BC, 0xBB82, 0xB550, 0xA626, 0xA8F4,
 251  0xF65A, 0xF888, 0xEBFE, 0xE52C, 0xCD12, 0xC3C0, 0xD0B6, 0xDE64,
 252  0x494C, 0x479E, 0x54E8, 0x5A3A, 0x7204, 0x7CD6, 0x6FA0, 0x6172,
 253  0x3FDC, 0x310E, 0x2278, 0x2CAA, 0x0494, 0x0A46, 0x1930, 0x17E2,
 254  0xA46C, 0xAABE, 0xB9C8, 0xB71A, 0x9F24, 0x91F6, 0x8280, 0x8C52,
 255  0xD2FC, 0xDC2E, 0xCF58, 0xC18A, 0xE9B4, 0xE766, 0xF410, 0xFAC2,
 256  0xB63F, 0xB8ED, 0xAB9B, 0xA549, 0x8D77, 0x83A5, 0x90D3, 0x9E01,
 257  0xC0AF, 0xCE7D, 0xDD0B, 0xD3D9, 0xFBE7, 0xF535, 0xE643, 0xE891,
 258  0x5B1F, 0x55CD, 0x46BB, 0x4869, 0x6057, 0x6E85, 0x7DF3, 0x7321,
 259  0x2D8F, 0x235D, 0x302B, 0x3EF9, 0x16C7, 0x1815, 0x0B63, 0x05B1
 260 };
 261
 262 static const guint16 crc16_ccitt_start = 0xFFFF;
 263 static const guint16 crc16_ccitt_xorout = 0xFFFF;
 264
 265 /* two types of crcs are possible: unreflected (bits shift left) and
 266  * reflected (bits shift right).
 267  */
 268 static guint16 crc16_unreflected(const guint8 *buf, guint len,
 269                                  guint16 crc_in, const guint table[])
 270 {
 271     /* we use guints, rather than guint16s, as they are likely to be
 272        faster. We just ignore the top 16 bits and let them do what they want.
 273     */
 274     guint crc16 = (guint)crc_in;
 275
 276     while( len-- != 0 )
 277         crc16 = table[((crc16 >> 8) ^ *buf++) & 0xff] ^ (crc16 << 8);
 278
 279     return (guint16)crc16;
 280 }
 281
 282 static guint16 crc16_reflected(const guint8 *buf, guint len,
 283                                 guint16 crc_in, const guint table[])
 284 {
 285     /* we use guints, rather than guint16s, as they are likely to be
 286        faster. We just ignore the top 16 bits and let them do what they want.
 287        XXX - does any time saved not zero-extending guint16's to 32 bits
 288        into a register outweigh any increased cache footprint from the
 289        larger CRC table? */
 290     guint crc16 = (guint)crc_in;
 291
 292     while( len-- != 0 )
 293        crc16 = table[(crc16 ^ *buf++) & 0xff] ^ (crc16 >> 8);
 294
 295     return (guint16)crc16;
 296 }
 297
 298 guint16 crc16_ccitt(const guint8 *buf, guint len)
 299 {
 300     return crc16_reflected(buf,len,crc16_ccitt_start,crc16_ccitt_table_reverse)
 301        ^ crc16_ccitt_xorout;
 302 }
 303
 304 guint16 crc16_x25_ccitt(const guint8 *buf, guint len)
 305 {
 306     return crc16_unreflected(buf,len,crc16_ccitt_start,crc16_ccitt_table);
 307 }
 308
 309 guint16 crc16_ccitt_seed(const guint8 *buf, guint len, guint16 seed)
 310 {
 311     return crc16_reflected(buf,len,seed,crc16_ccitt_table_reverse)
 312        ^ crc16_ccitt_xorout;
 313 }
 314
 315 guint16 crc16_0x5935(const guint8 *buf, guint32 len, guint16 seed)
 316 {
 317     return crc16_unreflected(buf, len, seed, crc16_precompiled_5935);
 318 }
 319
 320 guint16 crc16_0x755B(const guint8 *buf, guint32 len, guint16 seed)
 321 {
 322     return crc16_unreflected(buf, len, seed, crc16_precompiled_755B);
 323 }
 324
 325 guint16 crc16_0x9949_seed(const guint8 *buf, guint len, guint16 seed)
 326 {
 327     return crc16_reflected(buf, len, seed, crc16_precompiled_9949_reverse);
 328 }